Method of making metal carbides



Patented Sept. 6, 1932 UNITED- s rEs WINSTON r. STOOZDY, or wnI'rTIER, AND-THOR:RELLING, F BELVEDERE GARDENS,

CALIFORNIA, ASSIGNTORS TO STOODY COMPANY, OF WHITTIER, CALIFORNIA, .A'COR- PORATION OF CALIFORNIA METHOD or MAKING TAL cnnnrnns I g No Drawing.

This invention relates to a method of making carbides of metals, and more particularly to a method of making a tungsten carbide of any predetermined carbon content.

Tungsten carbide has long been known as an extremely hard, brittle composition, its hardness approaching and being comparable with that of the diamond.

The compound has been Y shaped, or has been combined with other metals and alloys, the metals and alloys acting as binders, for use as cutting tools for high speed practice. It has also been utilized alone or in combination with other metals and alloys as hard is: surfacing and insert materials to withstand extreme abrasive wear on oil well drilling bits and the like. 7

Tungsten carbide made by the fusion process in an electric furnace, has been'known since Moisson, Williams and other contemporaries; and later, Lohmann and others successfully made a tungsten carbide by a sintering process, i. e., the temperature range being well below the melting point of tungsten and carbon.

Attention has not been directed in the art to any particular carbide beyond the fact that a carbide was formed, the usual procedure being to add to the powdered tungsten an 0 abundance of carbon with a consequent forming of a tungsten carbide of formula WC with a theoretical carbon content of 6.12 per cent. Moisson, in his experiments on tungsten carbide in the electric furnace, fixes T a carbide of the formula W C with theoretical carbon content of 3.16, which later was afiirmed by But? and Wunsch in 1914, who also noted various eutectics which apparently occurred starting with a carbon content of 0.43 per cent.

without the use of any appreciable over- Application filed my 28, 1930. Serial 456.305.

abundance of carbon, and have evolved carbides'of various carbon content answering to the theoretical knowncarbides and eutectic points noted by former experimenters. The theory of the composition occurring at eutectic points containing less than 6.12 per cent combined or dissolved carbon, is not understood; but we believe the composition at these points is a conglomeratebf tungsten carbide; of the formula W C, and tungsten with a case'hardened shell'of'tungsten carbide of" formula W C, because after the tungsten carbide isseparated from the original composition, the remainder upongrinding, dissociates into tungsten and 72C, thereby denoting that all of the tungsten has not been completely changed into a carbide, but that some hasbeen merely coated with a cov ering or shell of carbide. These carbidesor eutectic pointswere obtained by varyingthe percentage. of carbonvin the mixture and sintering a gas furnace at temperatures rangingfl from' 17 00 F.2250. ..F. Eutectic points occurring at points above the combined or dissolved carbon content of 6.12 per cent, were noted at temperatures rangingfrom 2500? F. upwards in a glo-bar electricfurnace.

, The essence of our invention then consists in a .method of intimately mixing the tungsten powder and carbon so that'all the tungsten is in intimate contact with there'- quired amount'of carbon to produce the required tungsten carbide of specific carbon content,'and also means for controllingthe variables, viz, the percentage ofcarbon brought into intimate contact with "the metallic powder to be carbonized; theduration or timeof heat treatment; and the temperature at which the heat treatment W is made. i l

Our nvention consists in the steps of the method 'hereinafter' described and claimed;

To gas carbon black, we, add sufiicient petroleum oil to give therequired consistency to make a working paste. The mixture is given a long and thorough mixing in a paste-mixing machine used for intimately mixing powders, and has been found satisfactory. Other agglutinants such as sugar solutions, starch, resin and the like, have been used before, but they all have a tendency to increase the carbon content of the mixture not readily susceptible of control. It is an essential element of our method, that we use a distilled petroleum oil so that the carbon added to the tungsten, may be definitely weighed and determined, and no appreciable increase in the carbon content of the tungsten carbide composition will result. The petroleum oil being a distilled product, will distill oif upon subsequent heating, and leave no additional carbon in the tungsten carbide. Other volatile agglutinants which wholly volatilize during the subsequent heating, may be used. T 0 this paste is then added the proper proportion of very fine, pure tungsten powder, the resulting mass being then mixed thoroughly in a mechanical mixing machine for one to three hours, until every particle of tungsten has a coating of carbon. The product is then packed in refractory molds or crucibles, covered with a layer of graphite to prevent oxidation, and given a sintering heat treatment in either an electric or gas furnace of sufficient heat degree and length of time to insure the formation of the carbide.

Atypical charge which gives a tungsten carbide of theoretical carbon content of 6.12, would be as follows:

93.8 pounds tungsten powder.

6.2 pounds carbon contained in paste.

For any other lower carbides or eutectic points, the percentage would be varied so as to approach the theoretical carbon content of the lower carbides or eutectic points.

We have described our method relating to the making of tungsten carbides for eutectics of predetermined carbon content. However, the same method may be used in the production of carbides and eutectics of predetermined carbon content of metals other than tungsten. The temperature required for sintering in connection with metals other than tungsten, will, of course, vary with the particular kind of metal used.

Various changes may be made by those skilled in the art, in the steps of the method without departing from the spirit of our invention as claimed.

We claim:

1. A method of makingcarbides of metals, comprising making a paste of carbon with distilled petroleum oil, intimately mixing the paste with a finely divided metal, and sintering the mixture.

2. A method of making a carbide of tungsten, comprising making a paste of carbon 

